Nematode Host Meets Bacterial Pathogen

The nematode host Caenorhbaditis elegans encounters the bacterial pathogen S. marcescens. Natural selection imposed by the co-evolving pathogen led to the evolution and maintenance of bi-parental sex in the host population.
The host (C. elegans) and the pathogen (S. marcescens) were experimentally co-evolved to test the Red Queen hypothesis prediction that co-evolution with pathogens can select for the maintenance of cross-fertilization. Our results supported this Red Queen hypothesis prediction as co-evoloving S. marcescens selected for increased outcrossing in C. elegans.
Biologists at Indiana University (IU) have found that, although sexual reproduction between two individuals is costly from an evolutionary perspective, it is favored over self-fertilization in the presence of co-evolving parasites. Sex allows parents to produce offspring that are more resistant to the parasites, while self-fertilization dooms populations to extinction at the hands of their biological enemies.
To learn more, see the IU news story Sex, as we know it, works thanks to ever-evolving host, parasite relationships, IU biologists find. [Research supported by National Science Foundation grant DEB 06-40639.] (Date of Image: June 2011)
Credit: Levi Morran, Indiana University